Studies on the interactions among C ions activated modulator protein (A), its binding protein (I), cyclic nucleotide phosphodiesterase (PDE) and nucleotides. Kd and stoichiometry of A-I interaction were determined. I was found to bind nucleotides suggesting a complex regulatory role for I. An improved assay for PDE and kinetic methods for determining A-PDE and A-I affinities as well as on-off rates were developed. Selective elution technique was applied to purification of uridylyl transferase and uridylyl removing enzyme and found promising. Two sets of aspartate binding sites were shown for asparaginase. The finding may be important to the treatment of leukemia with asparaginase. Several methods related to the derivation of rate equations have been developed: A novel approach for computing the number of King-Altman patterns, an improved procedure for eliminating redundant terms, and a short cut for single-loop mechanisms.